Misc,
The Pan-STARRS1 $z>5.6$ Quasar Survey: III. The $z\approx6$ Quasar Luminosity Function
(2022)cite arxiv:2212.04179Comment: ApJ accepted, 40 pages, 19 Figures.
Abstract
We present the $z\!\approx\!6$ type-1 quasar luminosity function (QLF) based
on the Pan-STARRS1 (PS1) quasar survey. The PS1 sample includes 125 quasars at
$z\approx5.7-6.2$ with $-28M_1450łesssim-25$. Complemented by 48
fainter quasars from the SHELLQs survey, we evaluate the $z\approx6$ QLF over
$-28M_1450łesssim-22$. Adopting a double power law with an
exponential evolution of the quasar density ($\Phi(z)\propto10^k(z-6)$;
$k=-0.7$), we use a maximum likelihood method to model our data. We find a
break magnitude of $M^*=-26.38_-0.60^+0.79\,mag$, a faint end slope
of $\alpha=-1.70_-0.19^+0.29$, and a steep bright end slope with
$\beta=-3.84_-1.21^+0.63$. % Based on our new QLF model we determine the
quasar comoving spatial density at $z\!\approx\!6$ to be $n(
M_1450<-26)=1.16_-0.12^+0.13\,cGpc^-3$. In comparison with the
literature, we find the quasar density to evolve with a constant value of
$k\approx-0.7$ from $z\approx7$ to $z\approx4$. % Additionally, we derive an
ionizing emissivity of $\epsilon_912(z=6) =7.23_-1.02^+1.65\times
10^22\,erg\,s^-1Hz^-1cMpc^-3$ based on the
QLF measurement. Given standard assumptions and the recent measurement of the
mean free path of Becker et al. (2021) at $z\approx6$ we calculate an HI
photoionizing rate of $\Gamma_HI(z=6) 6
\times10^-16\,s^-1$, strongly disfavoring a dominant role of quasars
in hydrogen reionization.
